Psidium guajava L. has extensive use in folk medicine. The aim of this study was to quantify the levels of phenolic, flavonoids, antioxidant activity, leathality assay and antibacterial and antitumoral activities of the extract of P. guajava. In the dry guava extract there were high levels of phenolics (766.08 ± 14.52 mg/g), flavonoids (118.90 ± 5.47 mg/g) and antioxidant activity (87.65%). The LD50 was 185.15 µg/ml. The MIC value was 250 µg/ml for Streptococcus mutans, Streptococcus mitis and Streptococcus oralis. IC50 of the extract tested in the HeLa, RKO and Wi cell lines was 15.6 ± 0.8 µg/ml, 21.2 ± 1.1 µg/ml and 68.9 ± 1.5 µg/ml, respectively. The results of all analyses allow us to conclude that the dry extract of guava leaves has promising activity to be applied topically in the oral cavity or in the development of antitumor formulation or even be used as a functional food.

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All-trans retinoic acid (ATRA) has been studied for the treatment of cancer, including leukemia and breast cancer. This work aims to develop nanoemulsions (NE) loaded with a hydrophobic ion pair (HIP) of all-trans retinoic acid (ATRA) and a lipophilic amine, stearylamine (SA), and coated with hyaluronic acid (HA) to enhance anticancer activity and reducing toxicity. Blank NE was prepared by spontaneous emulsification and optimized prior to HIP incorporation. NE-ATRA was electrostatically coated with different concentrations of HA. Incorporation of ATRA-SA led to monodisperse NE with small size (129 ± 2 nm; IP 0.18 ± 0.005) and positive zeta potential (35.7 ± 1.0 mV). After coating with 0.5 mg/mL HA solution, the mean diameter slightly increased to 158 ± 5 nm and zeta potential became negative (-19.7 ± 1.2 mV). As expected, high encapsulation efficiency (near 100%) was obtained, confirmed by polarized light microscopy and infrared analysis. Formulations remained stable over 60 days and release of ATRA from NE was delayed after the hydrophilic HA-coating. HA-coated NE-ATRA was more cytotoxic than free ATRA for MDA-MB-231 and MCF-7 breast cancer cell lines, especially in the CD44 overexpressing cells. Blank coated formulations showed no cytotoxicity. These findings suggest that this easily-made HA-coated NE-ATRA formulation is a promising alternative for parenteral administration, thus improving the breast cancer therapy with this drug.

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